Re: [PATCH v6 05/34] ACPI / PPTT: Add a helper to fill a cpumask from a cache_id

[Jeremy Linton <jeremy.linton@arm.com>]

On 11/19/25 6:22 AM, Ben Horgan wrote:
> From: James Morse <james.morse@arm.com>
> 
> MPAM identifies CPUs by the cache_id in the PPTT cache structure.
> 
> The driver needs to know which CPUs are associated with the cache.
> The CPUs may not all be online, so cacheinfo does not have the
> information.
> 
> Add a helper to pull this information out of the PPTT.

Per V5:

Reviewed-by: Jeremy Linton <jeremy.linton@arm.com>>
> CC: Rohit Mathew <Rohit.Mathew@arm.com>
> Reviewed-by: Gavin Shan <gshan@redhat.com>
> Reviewed-by: Fenghua Yu <fenghuay@nvidia.com>
> Reviewed-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
> Tested-by: Fenghua Yu <fenghuay@nvidia.com>
> Tested-by: Carl Worth <carl@os.amperecomputing.com>
> Tested-by: Gavin Shan <gshan@redhat.com>
> Tested-by: Zeng Heng <zengheng4@huawei.com>
> Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
> Tested-by: Hanjun Guo <guohanjun@huawei.com>
> Signed-off-by: James Morse <james.morse@arm.com>
> Signed-off-by: Ben Horgan <ben.horgan@arm.com>
> ---
> Changes since v4:
> Same changes as previous patch in series
> do/while
> initialisation of acpi_cpu_id
> use new version of acpi_pptt_cache_v1_full
> 
> Changes since v3:
> Equivalent changes to the previous patch:
>   Tags dropped due to rework
>   Fallout/simplification from adding acpi_pptt_cache_v1_full
>   Look for each cache type before incrementing level
> ---
>   drivers/acpi/pptt.c  | 65 ++++++++++++++++++++++++++++++++++++++++++++
>   include/linux/acpi.h |  6 ++++
>   2 files changed, 71 insertions(+)
> 
> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
> index da49b56a1ef2..de5f8c018333 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -998,3 +998,68 @@ int find_acpi_cache_level_from_id(u32 cache_id)
>   
>   	return -ENOENT;
>   }
> +
> +/**
> + * acpi_pptt_get_cpumask_from_cache_id() - Get the cpus associated with the
> + *					   specified cache
> + * @cache_id: The id field of the cache
> + * @cpus: Where to build the cpumask
> + *
> + * Determine which CPUs are below this cache in the PPTT. This allows the property
> + * to be found even if the CPUs are offline.
> + *
> + * The PPTT table must be rev 3 or later,
> + *
> + * Return: -ENOENT if the PPTT doesn't exist, or the cache cannot be found.
> + * Otherwise returns 0 and sets the cpus in the provided cpumask.
> + */
> +int acpi_pptt_get_cpumask_from_cache_id(u32 cache_id, cpumask_t *cpus)
> +{
> +	int cpu;
> +	struct acpi_table_header *table;
> +
> +	cpumask_clear(cpus);
> +
> +	table = acpi_get_pptt();
> +	if (!table)
> +		return -ENOENT;
> +
> +	if (table->revision < 3)
> +		return -ENOENT;
> +
> +	for_each_possible_cpu(cpu) {
> +		bool empty;
> +		int level = 1;
> +		u32 acpi_cpu_id = get_acpi_id_for_cpu(cpu);
> +		struct acpi_pptt_cache *cache;
> +		struct acpi_pptt_processor *cpu_node;
> +
> +		cpu_node = acpi_find_processor_node(table, acpi_cpu_id);
> +		if (!cpu_node)
> +			continue;
> +
> +		do {
> +			int cache_type[] = {CACHE_TYPE_INST, CACHE_TYPE_DATA, CACHE_TYPE_UNIFIED};
> +
> +			empty = true;
> +			for (int i = 0; i < ARRAY_SIZE(cache_type); i++) {
> +				struct acpi_pptt_cache_v1_full *cache_v1;
> +
> +				cache = acpi_find_cache_node(table, acpi_cpu_id, cache_type[i],
> +							     level, &cpu_node);
> +
> +				if (!cache)
> +					continue;
> +
> +				empty = false;
> +
> +				cache_v1 = upgrade_pptt_cache(cache);
> +				if (cache_v1 && cache_v1->cache_id == cache_id)
> +					cpumask_set_cpu(cpu, cpus);
> +			}
> +			level++;
> +		} while (!empty);
> +	}
> +
> +	return 0;
> +}
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index be074bdfd4d1..a9dbacabdf89 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -1543,6 +1543,7 @@ int find_acpi_cpu_topology_package(unsigned int cpu);
>   int find_acpi_cpu_topology_hetero_id(unsigned int cpu);
>   void acpi_pptt_get_cpus_from_container(u32 acpi_cpu_id, cpumask_t *cpus);
>   int find_acpi_cache_level_from_id(u32 cache_id);
> +int acpi_pptt_get_cpumask_from_cache_id(u32 cache_id, cpumask_t *cpus);
>   #else
>   static inline int acpi_pptt_cpu_is_thread(unsigned int cpu)
>   {
> @@ -1570,6 +1571,11 @@ static inline int find_acpi_cache_level_from_id(u32 cache_id)
>   {
>   	return -ENOENT;
>   }
> +static inline int acpi_pptt_get_cpumask_from_cache_id(u32 cache_id,
> +						      cpumask_t *cpus)
> +{
> +	return -ENOENT;
> +}
>   #endif
>   
>   void acpi_arch_init(void);